High postpartum weight retention occurs in approximately 25 percent of young adult women and is an independent predictor of long-term weight gain, obesity, and obesity-related comorbidities. Preliminary efforts to reduce postpartum weight retention have met with some success but been limited by high attrition (30-40 percent) and failing to reach the populations at greatest risk (i.e., multiethnic, low income women). Innovative methods are needed to leverage women's naturally occurring motivation for weight control during the postpartum time period while captivating a greater proportion of the at risk population. Over the past decade, Internet use has increased exponentially in the US and most rapidly among young adult, low income, and minority sub-groups. Internet-based weight control interventions have been effective in promoting significant weight loss in obese populations. However, to date, no study has evaluated the effects an Internet-based program to prevent high postpartum weight retention in low-income women. We propose to develop and test the long-term efficacy of an Internet-based weight control program tailored for low-income postpartum mothers. We will be collaborating with the Women, Infants, and Children (WIC) program, which is a federally- funded community-based program providing nutritional support for low income multi-ethnic women. In this clustered randomized trial, 408 postpartum women with high postpartum weight retention will be randomized by clinic (N = 12) to either 12-month standard WIC or to a 12-month WIC Enhanced plus Internet-based postpartum weight loss program. Participants will be assessed at baseline, 6, and 12 months. The primary hypothesis is that the WIC Enhanced plus Internet program will produce significantly greater weight losses than the WIC Standard Care at 6 and 12 months; the intervention is also expected to increase the proportion of women who return to pre-pregnancy weight after 6 and 12 months. The project will provide a much-needed service to an underserved poplation and produce an empirically-based treatment package designed to be disseminated through WIC in the state of California and beyond.